(basically, we have a pattern very similar to 21st-99th, though recall that once we have three words in play, that et will only appears between the two highest denominations, so you will never see centēnsimus et decimus et tertius)

(also, to be explicit, everything continues to decline, where possible)

200th: ducentēnsimus, -a, -um

300th: trecentēnsimus, -a, -um

400th: quadrigentēnsimus-, -a, -um

500th: quīngentēnsimus, -a, -um

600th: sescentēnsimus, -a, -um

700th: septigentēnsimus, -a, -um

800th: octigentēnsimus, -a, -um

900th: nōngentēnsimus, -a, -um

1000th: mīllēnsimus, -a, -um

I’ll get to the 1000+ crowd eventually, though it involves multiplicative forms, so brace yourself.